Electrical measuring instrument.



J. W. RECORD.

ELECTRICAL MEASURING INSTRUMENT.

I APPLIGATION TILED D20. 23, 1912.

1.125.711. 'Patented Jan.19, 1915.

To all whom it may concern 8e it known that I, J 015m Wns'nronnmno RECORD, a subject of the King of Great Britain and 1re'land5 and a resident of Broedheath, near Manchester, England, have invented new and useful improve ments in Electrical Measuring Instruments, otzwli ch the following is a specification;

This invention relates to improvements in that type of moving coil electrical measuring instrument in which the coil in its traverso passes at one partand at one part only throu a space which is bounded by a junction a'pole piece with a magnet limb.

Such instruments as prevlously made have comprised two ring s aped pole pieces co-axially disposed relatively to each other, a coil encirc ng n g a d in its p ge around such ring pa ng he j ncti of the other ring with its magnet. In such a construction the coil when passing the polar junction is exposed to a magnetic field which is of difl'ercnt intensity to that to which it is elsewhere exposed in its path, owing to the oscape'of magnetic lines of force from such polar junction to the other pole piece,

such flux cutting th Outer 0 CIQSS ings of the coil as they pass through them.

My invention consists in nullifying or eliminating such polar junction magnetic flux, and thereby giving a magnetic field Which is of practically constant density throughout the Path of travel of the coil. This results in a very uniform graduation of-scale being possible and also results in a greater sensitivity of instrumentbecause the magnetic flux is much more usefully emplayed. This is accomplished by plac ng on the other side of the coil bearing pole piece, onother pole piece similar to that which is @lfflady established on one side of the coil pole piece. By doing this the magnetic flux which; has hitherto passed -,throug hv the space-bounded by the. magneti'o gap is usc fully conducted by the iron of the second pole piece to the place where it can be use: fully employed by passing directly through the annular gap between it and the coil.

bearing pole piece With this arrangement and the on quen n catl n o j limm tion of the flux fromthe spacehounded by the polar ju ction a m gnet c 'fie w i h s of P ac ic ly constant den ity t"rough 1 t l f peth f the 91 is oh eined. wi h'there- Specification of Letters geten Application flied Decoinher23, 191c. Serial No. 738,353.

' ther modification of the pole pieces.

the greduatiens ot thc inctrl'naent;

we: wnsmosamun snconn. or BBOADHEATE, nun-n nancnns'mn, .ENG'LAND. announcer. nnesunme msrtnunlinr.

. scald-are about constant throu hout the range of the instrument. Additnal sensitivity andregularity of movement of the coil may be obtained by. giving the cooperating and relatively laterally disposed coiiperailing pole pieces the dimensions and forms hereinafter described.

The accompanying drawings illustrate how my invention may be carried into efiect.

Figure 1 is a plan View of one form of the magnet and pole pieces of the instrument. Fig. 2 illustrates the same magnet and pole pieces in elevation. Fig. 3 illustrates in elevation a modification in the pole pieces. Fig. 4.: represents in section a i ur 1g. 5 is a view in elevation of another magnet with still further modified pole pieces. Fig. 6 is a view in elevation of a magnet with further modifications in the pole pieces. F1g. 7 is a view of one of the coiiperating' pole pieces of Fig. 6 detached from its magnet. Fig. 8 is a View of a ringshaped pole piece detached from its magnet. Fig. 9 illustrates a modification in the mode of mounting the moving coil. L'li e letters of reference indicate like parts where they occur in the different figures.

Referring first to Figs. 1 and 2. A is the permanent magnet having a ring shaped pole piece N of one polarity. The moving coil B is; placed upon and passes through the pole piece l and rotates upon and with the spindle'C. and S are pole ieces of opposite-polarity to. N and place one on each side of it; y The spindle C passes through all the pole pieces. The pole pieces S S are placed sufficiently far from the pole piece N to permit free passage or movement of the sides of the coil as it moves frOm one to another ofits two extreme positions shown in broken and full lines in Fig.

- 8, but areotherwise as close as they can be to the pole pi ege Nan'd to the coil B to give as great an intensity as possible to the magnetic field in vv'zhichthe coil moves.

In Figs. land 2 the pole pieces 8 S are shown as being ring shaped and oi the same diameter as the ring pole piece But the pole pieces S W may be of larger diameter than N'as shownin Fig. 3. v-Vl ith the larger pole piepos of Fig. 3 the cross windings of the boil B which pass over adence-cos the periphery of the ring N are Patented Jen. is, new. j

- which the pole pieces S S are connected piece N.

always in an active and constant magnetic field. They are not always in an active and constant field with the dimensions of pole pieces shown in Figs. 1 and 2, because when passing between the points 1 and 2 indicated in Fig. 2 thQ'CIOSS windings are exposed to magneticflux from the necks by to the magnet and are not exposed to such flux when passing between either of the points 1 or 2 and the neck n of the pole In the figures already referred to the various pole pieces have hadtheir opposed faces flat and parallel to each other. In the form of pole pieces shown in Fig. 4 each of the pole pieces S S has a concave inner face and the outer faces of the pole piece N are suchcross windings are always in an active 1 magnetic field.

It willbeseen clearlyfrom Fig. 8 that theatre of movement'of the coil is only also the pole piece S gular area limited by the coil coming into contact with one side or other of the neck '22 of the pole piece N. The two extreme positions of the coil are shown by representations of. the coil in broken and full lines. It will be seen that there is thus an angular area g of the pole piece N which the coil never moves over. The magnetic flux which takes place between this angular area and the opposite portions of the pole pieces S S is therefore Wasted.

The pole piece S shown in Fig. 6 (and I which is not visible) has a gap cut in and through it bounded by the walls D D, this'gap corresponding in form and area andbeing opposite to the angular areay of the pole pieceiN. With the gap thus formed there is no (or very little) magnetic flux from the described ang ofthe pole piece N, and the flux which has hitherto been wasted atthis part is diverted to and utilized in those portions of the annular spaces between pole pieces which are traversed by the coil.

The pole piece Fig. 7.

T he magnetic gap bounded by the walls need not have the form and area of the angular area 'y of the pole piece N. It may have other forms and still achieve the same object of preventing magnetic flux from the angular area 1 A magnetic gap is only shown as being formed m a rectangular pole piece S or S they may be of any other desired S is shown detached in of Figs. hand 7 but it may also be formed in the ring shaped pole-pieces S S 0t Figs. 1 to 4.

Thering shaped pole piece N may be di-' duplicate and rotate around outer rings S 8. See Fig. 9..

.In Fig. 2 ,a,p0inter or needle E attached to'the spindle'C is illustrated, and a disk graduated for showing variations of cur rent. The markings on the disk are at regular distances, ornearly so, apart to indicate like variations in the strength of the current passingt-hrough' the coil. I

V F F are spiral tension springs by which the spindle and coil are held in or returned to their zero position, and these springs mayserve to conduct current to' and from the coil, or other connecting devices maybe used. y 1

What I'claim is I 1. In an" electrical'.measuring instrument, the combination with a magnet having two magnetic limbs to which the pole pieces are adapted to be secured, an annular pole piece secured to one of said limbs, a coil mounted for angular movement surrounding said pole piece, said othermagnetic limb beingin a positionfor its flux to effect the coil in a part only of its angular movement, of two pole'pieces securedto said last named limb one oppositeeach face of the annular pole piece and arranged in close proximity there to to thereby'prevent the flux from said last mentioned magnetic limb efiecting the coil and rendering the flux which'efi'ects the coil substantially uniform throughout the angular movement thereof.

2. In an electrical measuring instrument, the combination with a magnet having two magnetic limbs to which the pole pieces-are adapted to be secured, an annular secured to one of said limbs, a coil mounted for angular movement surrounding said pole piece, said other'magnetic limb being in a position for its flux to effect the coil in a part only of its angular movement, of two pole piecessecured to said last named limb one opposite each face of the annular pole piece and of sufficient size to overlie the same to thereby prevent the flux from the magnetic limb effecting the coil and to render the flux which effects the coilsuba stantially uniform throughout the angular movement of the same.

3. In an electrical measuring instrument, the combination with a magnethaving two magnetic limbs to which the pole pieces are adapted to be-secured, an annular pole piece pole piece I piece is secured to the magnetic limb to gag form a magnetic gap whereby the flux from the last named magnetic limb is prevented from effecting the coil during its angular l5 movement.

In witness whereof I have hereunto set my hand in the presence of two subscribing Witnesses.

JOHN WESTMORELAND RECORD.

Witnesses:

WILLIAM Gno. Hers, JOHN OConnm. 

